1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to a packet data communication method for a CDMA communication system.
2. Description of the Related Art
Code division multiple access (CDMA) mobile communication systems are based on the IS-95 standard which mainly supports voice service. In the near future, mobile communications will be performed in accordance with the IMT-2000 (International Mobile Telecommunication-2000) standard. The IMT 2000 standard provides not only voice service but also high speed packet service. For example, the IMT-2000 standard supports high quality voice service, moving picture service, Internet search service, etc. The CDMA mobile communication system includes a forward link for transmitting a signal from a base station (BS) to a mobile station (MS) and a reverse link for transmitting a signal from the mobile station to the base station.
During the packet service, an existing CDMA mobile communication system generates packet data at a burst and frequently repeats a dormant state where data is not transmitted. Accordingly, it is anticipated that a mobile communication system in the near future would connect a channel only when there is data to transmit. That is, taking into consideration limited radio resources, capacity of the base station and power consumption of the mobile station, the base station releases the channel when there is no data to transmit, in order to secure the channel for communication with the another mobile station, and then quickly reconnects the channel when there is data to transmit. A conventional method for transmitting packet data is illustrated in FIG. 1.
Channels used in the CDMA mobile communication system are classified into physical channels and logical channels. The logical channels are established in an upper layer of the physical channels, and several logical channels can be established for one physical channel. Upon release of a physical channel, the logical channels established for the released physical channel are automatically released. For establishing a logical channel, establishing a physical channel is not always necessary. For example, in the case where a physical channel to be established for a logical channel has already been established for another logical channel, a required operation is to simply assign the logical channel to the established physical channel.
The physical channels can be classified into dedicated channels and common channels according to features. The dedicated channels are exclusively used for communication between the base station and the mobile station, and include a fundamental channel (FCH), a dedicated control channel (DCCH) and a supplemental channel (SCH). The fundamental channel is used for transmitting voice signals, data and signaling messages. The dedicated control channel is used for transmitting data and signaling messages. The dedicated control channel supports a discontinuous transmission (DTX) mode for transmitting data only when there is data to transmit, generated from the upper layer. For such a feature, the dedicated control channel is suitable for a control channel established to provide an efficient packet service. The supplemental channel is used for transmitting a great quantity of data, and is compatible with the IS-95B standard.
In addition, the physical channels include the common channels which are used in common between one base station and multiple mobile stations. A physical common channel for the forward link for transmitting a signal from the base station to the mobile station is called a paging channel, and a physical common channel for the reverse link for transmitting a signal from the mobile station to the base station is called an access channel. These common channels are also compatible with the IS-95B standard.
The common logical channels established in the upper layer of the common physical channels are classified into a dedicated signaling channel (dsch) and a dedicated traffic channel (dtch). The dedicated signaling channel can be assigned to the fundamental channel and the dedicated control channel, which are both physical channels. The dedicated traffic channel can be assigned to the fundamental channel, the dedicated control channel and the supplemental channel. As can be hinted from the names, the dedicated signaling channel is used for exchanging a control signal between the base station and the mobile station, and the dedicated traffic channel is used for exchanging user data between the base station and the mobile station.
For the forward link, the common logical channels are established in the upper layer of the paging channel; for the reverse link, the common logical channels are established in the upper layer of the access channel.
FIG. 1 is a diagram illustrating state transitions of a data service entity in a CDMA mobile communication system. FIG. 2 is a diagram illustrating state transitions between substates of the data service entity which occur when data to be transmitted is generated in a suspended state 150 of FIG. 1.
When the data is generated in the suspended state 150, the state transitions occur equally in the base station and the mobile station. For simplicity, a party transmitting the data will be referred to as a transmission party and a party receiving the data as a reception party.
Referring to FIG. 1, in a packet null state 110, the base station and the mobile station are powered up and wait for a data service request to be received from the other party. When a packet service request is received in this packet null state 110, a transition from the packet null state 110 to an initialization state 120 takes place.
In the initialization state 120, forward and reverse control channels required for data transmission are established. Here, for the dedicated physical channel, the fundamental channel or the dedicated control channel is established; for the logical channel, the dedicated signaling channel, which is a logical channel between the base station and the mobile station, is established in the upper layer of the fundamental channel or the dedicated control channel. Upon establishment of the dedicated signaling channel, the base station negotiates with the mobile station about specification of a service to be provided. A service specification determined through such a negotiation is referred to as a “service option”. After negotiation for the service option, a data service entity establishes a dedicated traffic channel required for transmitting user data and then, transitions to an active state 140. However, upon failure of the initialization process, the data service entity transitions back to the packet null state 110.
In the active state 140, the data is transmitted using the dedicated traffic channel. When the data service entity can use the dedicated control channel in the active state after setting the service option, the base station and the mobile station perform RLP (Radio Link Protocol) and PPP (Point-to-Point Protocol) initialization processes. When there is no data to be transmitted for a predefined time T—active in the active state 140, a transition from the active state 140 to a control hold state 130 occurs, releasing the dedicated traffic channel. Here, a quantity of data to be generated henceforth is expected; if it is judged that the data to be transmitted will not be generated for a long time, a transition can take place to a suspended state 150 or a dormant state 160 directly, without passing through the control hold state 130.
In the control hold state 130, the service option, RLP-related information and PPP-related information are preserved in the base station and the mobile station, and the dedicated signaling channel is established. In this state, if data to be transmitted is generated again within a predefined time T—hold, the data service entity establishes the dedicated traffic channel and then transitions back to the active state 140 in order to transmit the generated data. However, if data is not generated within the time T—hold, the data service entity releases the dedicated control channel and then transitions to the suspended state 150. Even in this case, a quantity of data to be generated henceforth is expected; if it is judged that the data to be transmitted will not be generated for a long time, it is possible to directly transition to the dormant state 160, without passing through the suspended state 150.
In the suspended sate 150, the fundamental channel or the dedicated control channel, which is a physical channel assigned to the mobile station, is released and the corresponding logical channels, i.e., the dedicated signaling channel and the dedicated traffic channel are also released. In this state, communication with a base station is performed using the common signaling channel established for the paging channel and the access channel, which are physical channels being shared by multiple mobile stations. However, in the suspended state 150, the service option, the RLP-related information and the PPP-related information are still maintained in the base station and the mobile station. When user data to be transmitted is generated again within a predefined time T—suspended in the suspended state 150, the dedicated control channel and the dedicated traffic channel are simultaneously established and a transition back to the active state 140 occurs. However, if data is not generated for the time T—suspended, a transition to the dormant state 160 takes place.
In the dormant state 160, only a point-to-point protocol (PPP) for the data service is open and all other call-related information disappears. Even in the dormant state 160, if it is necessary to transmit data again within a predefined time T—dormant, a transition to the active state 140 occurs after assignment of the dedicated signaling channel. However, when data to be transmitted is not generated within the predefined time T—dormant, even the PPP information is released and then a transition to the packet null state 110 takes place.
Referring to FIG. 2, the suspended state 150 includes a virtual traffic substate 153 and a slotted substate 156. Both in the virtual traffic substate 153 and the slotted substate 156 of the suspended state 150, the service option and the RLP information are maintained in the base station and the mobile station. A transition to the virtual traffic substate 153 of the suspended state 150 takes place, in the case where data to be transmitted is not generated within the time T—hold in the control hold state 130 and a virtual active set needs to be maintained even in the suspended state 150.
On the contrary, a transition to slotted substate 156 takes place, in the case where data to be transmitted is not generated within the time T—hold in the control hold state 130 and the virtual active set does not need to be maintained in the suspended state 150. In the virtual traffic substate 153, the virtual active set is maintained to assist prompt assignment of a traffic channel. Here, the virtual active set is a list in which a strength of the forward pilot channel is recorded, the list being managed simultaneously in both the base station and the mobile station even in a state where the common channel is in use.
To manage the virtual active set in the virtual traffic substate 153, the mobile station measures a strength of the pilot channel transmitted from an adjacent base station, and sends, when the measured strength satisfies a predetermined threshold, a message notifying this condition to the base station. Upon receipt of the message, the base station sends back an acknowledge message to the mobile station. Data for maintaining the virtual active set is exchanged via forward and reverse common signaling channels, f/r-csch. A virtual traffic timer counts a holding time T—virtual of the virtual traffic substate 153 and is prepared (or included) in the system. When data to be transmitted is generated within the time T—virtual in the virtual traffic substate 153, a transition to the active state 140 takes place in order to transmit the generated data.
However, when data to be transmitted is not generated within the time T—virtual in the virtual traffic substate 153, a transition back to the slotted substate 156 takes place. In the slotted substate 156, the paging channel being a physical channel, to which the forward common signaling channel (f-csch) being a logical channel is assigned, is monitored in a slotted mode (or on a time-division basis) for reducing power consumption of the mobile station, and the virtual active set is not maintained. Similarly, when data to be transmitted is generated within a predefined time T—slotted in the slotted substate 156, a transition to the active state 140 takes place in order to transmit the generated data. However, when data is not generated within the time T—slotted in the slotted substate 156, a transition to the dormant state 160 takes place. In this procedure, the service option and the RLP information which have been managed in the base station and the mobile station are all released. To restart data transmission in the suspended state 150, the traffic channel and the control channel should be reassigned, and a channel renegotiation should be made between the base station and the mobile station. In the renegotiation process, a latency occurs because of the signaling overhead.
It is further still another object of the present invention to provide a method for increasing a channel utilization efficiency and a data communication speed, in which a transmission party includes a virtual traffic substate and a slotted substate where a common traffic channel is established, segments data to be transmitted by a frame length of the common traffic channel and then transmits the segmented data via the common traffic channel; a reception party then receives the segmented data via the common traffic channel and reassembles the received segmented data.
In accordance with one aspect of the present invention, when data to be transmitted is generated in a suspended state, a length of the generated data is compared with a reference length for normal data transmission in an active state. When the generated data is shorter than the reference length, a generation frequency of the data generated in the suspended state is compared with a reference generation frequency for normal data transmission in the active state. If the generation frequency of the data generated in the suspended state is lower than the reference generation frequency, a transition to a burst substate occurs to segment the data by a frame length of a common traffic channel and then the segmented data is transmitted via the common traffic channel. However, if a burst substate does not exist, the segmented data is transmitted via a previously assigned common traffic channel.
In accordance with another aspect of the present invention, when data to be transmitted is generated in a suspended state, a transmission party segments the data into frames having a specified length and transmits the segmented data via a previously established common traffic channel. Upon reception of the transmitted segmented frames in the suspended state, a reception party reassembles the received frames and transmits the reassembled frame to an upper layer.